Chapter 5: Phthalocyanines in Cancer-Imaging and Therapy

Photodynamic therapy (PDT) is a form of phototherapy using nontoxic, light-sensitive compounds that upon exposure to light generate toxic, reactive oxygen species (ROS) targeting malignant and other diseased cells (phototoxicity). Most modern PDT applications involve three key components: A photosensitizer (PS), a light source and molecular oxygen. PDT is used clinically to treat a wide range of medical conditions, including wet age-related macular degeneration and various cancers, and it is recognised as a treatment strategy that is both minimally invasive and minimally toxic. Phthalocyanines (Ps) and its derivatives are structurally related to porphyrins. They have been advanced as PS for PDT due to their strong absorption in the visible region (strong Q band bands around 670 nm) and high quantum yield for the generation of ROS. To optimize PDT efficacy for selected applications their lipophilic and hydrophilic properties can be modulated by modifying peripheral substituants and the central metal ion. Furthermore their target specificity can be improved through conjugation to biomolecules. In this chapter we address potential structure-activity relationships of phthalocyanine-based PS and review their clinical potential.